Surface binding of alamethicin stabilizes its helical structure: molecular dynamics simulations

Area of Science:

• Biophysics
• Computational Biology
• Membrane Biophysics

Background:

• Alamethicin is an amphipathic alpha-helical peptide known to form ion channels.
• Initial binding to lipid bilayer surfaces is a critical step in alamethicin channel formation.

Purpose of the Study:

• To compare the structural and dynamic behavior of alamethicin in water versus when bound to a phosphatidylcholine bilayer surface.
• To investigate the role of lipid bilayer interactions in stabilizing alamethicin's alpha-helical conformation.

Main Methods:

• Utilized 2-nanosecond molecular dynamics simulations.
• Simulated alamethicin in aqueous solution and at the surface of a lipid bilayer.
• Analyzed peptide structure, helicity, and hydrogen bonding patterns.

Main Results:

• In water, alamethicin's helix unfolded significantly, leading to a compact structure.
• At the bilayer surface, helicity loss was limited to the C-terminal region, preserving the rod-like shape.
• Peptide/lipid hydrogen bonds partially replaced peptide/water hydrogen bonds at the bilayer surface.

Conclusions:

• Alamethicin's alpha-helical structure is stabilized at the lipid bilayer surface.
• Stabilization occurs even with only headgroup interactions, without penetrating the hydrophobic core.
• Bilayer surface interactions contribute to maintaining the peptide's conformation essential for ion channel formation.